This invention relates to an idling noise silencer for a marine propulsion unit and more particularly to an improved arrangement for silencing the idling noises of a marine propulsion unit and for preventing corrosion through the use of a sacrificial anode.
The treatment of exhaust gases in marine propulsion units and particularly outboard drives is a troublesome one. It is well known to discharge the exhaust gases from the powering engine through an underwater exhaust gas discharge so as to utilize the body of water in which the watercraft is operating as a silencing medium. Although this is a very acceptable and effective way for silencing exhaust gases under high speed running conditions, it does present certain problems in connection with low speed exhaust gas discharge. With an outboard motor, it is the common practice to provide a separate, above the water, exhaust gas discharge which has its own silencing system for treating the idling exhaust gases. With inboard/outboard drives, on the other hand, the powering engine usually has a larger displacement and the treatment of the exhaust gases during idling present different problems. It has been proposed with such arrangements to employ a further auxiliary exhaust gas discharge which is also underwater when the boat is traveling at low speeds but is less deeply submerged than the high speed exhaust gas discharge. Although this does provide good silencing, the exhaust gases tend to emanate in large bubbles which can cause objectionable noise.
It is, therefore, a principal object of this invention to provide an improved exhaust gas discharge for a marine propulsion unit.
It is a further object of this invention to provide an improved underwater exhaust discharge for a marine outboard drive.
It is a yet further object of this invention to provide an improved silencing arrangement for the idling gases of an outboard drive unit.
In addition to the problem of handling the exhaust gases in marine propulsion units, there is also the problem of galvanic corrosion. These problems are particularly acute when operating in a marine environment since the salt water greatly accelerates the effects of galvanic corrosion. Although it has been proposed to employ sacrificial anodes, the placement of the anode can cause considerable difficulties. The anode should be placed in an area where it will be in contact with the cooling water that flows through the engine and also should be positioned in an area where the galvanic action is most likely to occur. Inconsistent with these requirements is the desire to position the sacrificial anode in an area where it can be conveniently and quickly replaced.
It is, therefore, a still further object of this invention to provide an improved sacrificial anode construction for a marine outboard drive.
It is another object of this invention to provide an improved, readily removable and easily serviced sacrificial anode for a marine outboard drive.